Integrally bladed rotors (IBR's) for gas turbines are often called “blisks” or “blings”, depending on the cross-sectional shape of the rotor. A disk-shaped rotor having integrated blades is called “blisk” (bladed disk), a ring-shaped rotor having integrated blades is called “bling” (bladed ring). IBR's are formed from a single piece of material that includes the hub, the disk and all the rotor blades, in contrast to conventional rotors in which multiple individual blades, formed separately from the hub and disk, are mounted on the disk using a mechanical connection.
Several conventional methods for the manufacture of integrally bladed rotors have been used. These methods include milling methods as well as chemical or electrochemical discharge methods to remove material from portions of the material to define flow channels and blades. One example of a conventional milling method for the manufacture of integrally bladed rotors is disclosed in the U.S. Pat. No. 6,077,002. Conventional manufacturing methods for IBR's tend to be difficult and time consuming to carry out, and often require manual finishing steps, resulting in an expensive manufacturing process for integrally bladed rotors.
The present invention provides a method for the manufacture of components for gas turbines made of difficult-to-cut materials, by forming recesses with one or more side walls in a workpiece block of the material. The exemplary method is well suited for manufacturing integrally bladed rotors used in compressor and turbine stages of gas turbines, especially for use in aircrafts engines. The recesses formed according to the exemplary method define the flow passages between the rotor blades, and the side walls of the recesses define the opposing concave and convex surfaces of adjacent rotor blades. Accordingly, the contours of the recesses define the airfoil shape of the blade surfaces, and thus the radial cross section of the flow path between the blades. IBR's are well suited for use in axial flow compressors and turbines of aeronautical engines, however, other applications may also be envisioned that would benefit from the manufacturing methods of the present invention.
Material in the region of the flow channels is initially removed, according to an exemplary embodiment of the invention, by a drilling process. After the drilling process is completed, the removal of material in the region of the flow channels continues with an initial milling process, which more accurately defines the shape of the blade surfaces. These two initial drilling and milling steps are similar to the steps described in U.S. Pat. No. 7,225,539, which is hereby incorporated by reference in its entirety. The combination of a drilling process followed by a milling process for material removal reduces significantly the manufacturing time and results in a less expensive manufacturing of the IBR's than other manufacturing processes. However, after these steps the blades are still not sufficiently smooth and their shape is not sufficiently accurate to be ready for use.
To refinish the blades, an additional finishing milling step is carried out according to exemplary embodiments of the present invention. This step takes place after filling the nearly formed flow passages with a dampening material. This additional milling step produces blades that have the desired accurate shape, and the desired surface finish. A benefit of the exemplary method according to the invention is that there is no need for any manual steps in finishing the blades, such that the entire IBR manufacturing process is automated.
In accordance with an exemplary embodiment of the present invention, the drilling process may be carried out in such a way that a drilling tool removes material in a flow-wise direction from the flow passages between pairs of blades to be formed in the workpiece material. In an IBR, the shape of the flow passage between two adjacent blades may vary considerably in the radial direction, from the hub to the tip of the blades. Accordingly, multiple flow channels may be defined in the radial direction within each flow passage, between hub and tip. According to the invention, the axis of the drill-holes may be computed for each radially distinct flow channel, and may be selected to be approximately parallel to the flow direction through that flow channel. For each flow channel, at least one center line of the flow channel may be calculated, for example from the contours of the side-walls defining the flow channel, which correspond to the opposing surfaces of two adjacent blades.
The exemplary drilling process is performed so that the axis of each drill-hole is approximately parallel to the center line that approximates the center of the flow channel to be manufactured. For example, an inlet-side opening of each drill-hole may be located adjacent to the leading-edges of the blades defining the flow channel to be manufactured, and the outlet-side opening of each drill-hole may be located adjacent to the trailing-edges of the blades defining the flow channel. Those of skill in the art will understand that the drill holes may be started at the trailing edge, and may extend to the leading edge.
Alternatively, according to another exemplary embodiment of the present invention, the drilling process may be performed in a way that a drilling tool removes material in a cross-flow direction of each flow channel. In this case, the axis of the drill-holes may be approximately perpendicular to the flow direction through the flow channel to be manufactured. The drilling tool thus removes material by drilling holes starting from the outside diameter of the rotor, at the tip, generally in a radial direction towards a hub of the rotor. The center line of the flow channel may be determined as explained above, and the drill may be operated in a generally perpendicular direction to the center line.
Following completion of the drilling process, as described above, the removal of material to form the flow passages may continue with an initial milling process. In this step according to an exemplary embodiment of the invention, a milling tool is used to remove additional material that remains around the blades after the drilling process. This step defines more accurately the shape of the flow passages and of the surfaces of the blades defining the flow passages. The blade resulting after this initial or coarse milling step is still rough, and does not have a sufficiently accurate shape and sufficiently smooth surface to be used in the turbine engine.
In one exemplary embodiment, the initial milling step is carried out along an axis of the milling tool or cutter that is generally perpendicular to the center line approximating the center of the flow channel being manufactured. For example, the milling tool may operate along a generally radial axis, so that it extends from the tip towards the root of the blades. The milling tool may be moved along the concave and the convex surfaces of each blade, and around the leading edge and trailing edge thereof, to remove excess material and more accurately shape the blades and the flow channel.
Because the initial milling step does not produce blades that are ready for use, an additional step is carried out, according to exemplary embodiments of the invention, to produce a better finish and a more accurate shape for the blades. For example, mismatches, waviness and chatter due to the flow-wise drilling and initial milling sequence may be removed or reduces by the additional finishing milling step. This additional automated step removes the need to manually finish the blades after the initial drilling and milling steps, and also increases the accuracy and quality of the finish. According to exemplary embodiments of the invention, the additional step may be an I-flow milling process, in which the finishing milling step is carried out after a damping material is used to fill all the flow passages between the blades.
Prior to the finishing milling step, the rough shape of the blades and of the flow passages are already defined. A damping material is then inserted in the flow passages, between adjacent pairs of blades, to completely surround each of the compressor or turbine blades. This material, for example, may dampen vibrations of the blades during machining. The milling cutter tool is then used to refinish the blade surface, removing both the damping material and the blade material to produce a smooth and accurate shape of the blade surfaces.
In one exemplary embodiment, the milling tool is moved along one surface of a first blade defining the flow path, then across the flow path and along the opposite surface of the adjacent blade. The milling procedure may start at the leading edge, concave side of a blade, travel along the concave surface of the blade to the trailing edge, move across to flow passage to the convex side of the adjacent blade, and then travel to its leading edge along the convex surface. The opposite routing of the milling tool may also be used to obtain substantially the same results. The milling tool may be moved as explained above to ensure that for each blade, at least one surface is milled while the opposite surface is still encased in the damping material, to reduce or prevent vibration and deflection of the blade that may result in an inadequate blade finish. According to embodiments of the invention, the path of the milling tool is selected to maximize the damping effect of the damping material, by delaying the removal of the material from one side of the blade while the other side is being finished. Thus, to maximize the damping effect, the finishing milling tool may move along a path that preferentially mills one surface of a blade while the other surface of the same blade is in contact with the damping material.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings